In glass applications such as liquid crystal panels, optical communication devices for instance optical filters and optical switches, recording medium, halogen and High Intensity Discharge (HID) lamps etc. the consistency of the glass substrate properties is quite critical. High-energy laser systems employ multiple large pieces of optical quality glass, sometimes thousands of large size laser glass pieces, and it is imperative for the pieces to have consistent optical quality. Glass compositions, similarly to fused quartz compositions, are characterized by a few fundamental properties affecting the manufacturing of or the properties of products employing the compositions, i.e., viscosity, % transmission, OH level to name a few. The effect of OH (hydroxyl) on viscosity of glass or quartz is widely known. FIG. 1, for instance, illustrates the viscosity curves of high purity quartz made with various OH concentrations. As seen from the Figure, viscosity of glass drastically drops with increased hydroxyl concentration. If glass or quartz has batch-to-batch or within-batch variations in the OH level, it will result in inconsistent manufacturability and product quality. From a lamp manufacturer's perspective, variations in the glass properties impact the yields of the high-speed lamp production lines, requiring undesirable and frequent adjustments made to the equipment to account for the variations in the glass properties.
Almost all arc discharge lamps and many high intensity filament lamps, such as tungsten-halogen lamps, emit ultraviolet (UV) radiation which may be harmful to human eyes and skin. As disclosed in U.S. Pat. Nos. 2,895,839; 3,148,300; 3,848,152; 4,307,315 and 4,361,779, lamps have been developed having a light source which emits both UV and visible light radiation enclosed within a vitreous envelope of fused quartz. U.S. Pat. Nos. 2,221,709; 5,569,979; 6,677,260 disclose fused quartz compositions containing UV-absorbing materials, or dopants as they are called, in the form of tubings or rods for use in making lamps, e.g., as lamp envelopes with properties to absorb UV radiation.
U.S. Patent Publication No. 20040063564A1 discloses a composition useful for forming glass substrates for use in information recording medium, with desirable properties such as specific linear thermal expansion coefficient, fracture toughness, and a predetermined surface hardness. In applications for making bulk glass articles such as fiberglass, it is also useful to have consistency in the glass compositions to obtain the desired ranges of properties such as viscosities, humidity resistance, and the like. U.S. Patent Publication No. 20020077243A1 discloses a composition for making glass fiber filters for use in micro-electronic clean room environments.
Due to the bulk volume of the feedstock making up the glass composition, there is a wide batch-to-batch variation in glass compositions as well as in the properties of products made from glass compositions of the prior art. It is important to have consistent properties in a glass composition such that products made thereof have properties that are uniform or varying in a narrow range. Additionally, the consistent properties allowing manufacturers to run production lines with minor or no adjustments in the line, for high productivity and consistently good glass products. In one aspect, the invention provides a novel glass composition and a method for making glass products with uniform properties, as measured by the standard deviation.
Glasses also find application in pharmaceutical packaging. There has been a recent trend in the pharmaceutical market toward the increased use of biological (protein-based) drugs that are more “sensitive” than traditional drugs. With these types of drugs, the topic of drug/container interaction becomes increasingly important due to the lower stability of these drugs and their propensity to degrade during storage, especially when formulated as a liquid. Because of this, extractable substances (e.g. dissolved cations) coming from the pharmaceutical packaging container can cause issues with regard to efficacy and purity with these drugs (including drug instability, toxicity, etc). A Review of Glass Types Available for Packaging, S. V. Sangra, Journal of the Parenteral Drug Association, March-pr., 1979, Vol. 33, No. 2, pp. 61-67.
Cationic extraction from traditional glasses used in pharmaceutical packaging can create issues with the purity and/or effectiveness of such protein-based drugs. The mechanism of cationic extraction is typically hydronium/alkali ion exchange that causes a pH increase, which is then followed by bulk dissolution, especially in Type I (e.g., borosilicate, such as Schott Fiolax®) and Type II (soda lime silicate) glasses. The poor chemical durability of these glasses arises from the fact that soluble cations, such as Na+, Li+, K+, Mg2+, Ca2+ and/or Ba2+ are used to flux these glasses to achieve a suitably low working point temperature that makes them highly processable with standard glass melting equipment (see, e.g., U.S. Pat. Nos. 5,782,815 and 6,027,481).
Glass particle generation due to delamination is one of the major concerns in pharmaceutical packaging industries when Type I and Type II glasses are used as the container for pharmaceutical products. Delamination occurs when top layers of a glass separate at a scale that is barely visible or invisible to the naked eyes as shown in FIG. 1 of Ronald G Iacocca, “The Cause and Implications of Glass Delamination”, Pharmaceutical Technology, 2011, pp s6-s9, the disclosure of which is incorporated herein by reference in its entirety. The particles become suspended in drug solutions, posing a serious risk to the consumer.
Glasses without chemical modifiers (e.g., alkali metals, borates, alkaline earth metals) such as fused quartz glass are preferable from a chemical purity (low extractables) and chemical durability perspective, but such glasses may be difficult to manufacture due to the high processing temperatures required (typically >2,000° C.). Even when fused quartz glasses can be melted and formed into tubing, it is then often difficult to flame convert them into pharmaceutical packages (vials, syringe barrels, ampoules, etc), due to a high working point temperature (>1,700° C.). Thus, such glasses have generally not been used to manufacture pharmaceutical packaging. U.S. Pat. Nos. 6,200,658 and 6,537,626 show that efforts have been made to coat the interior surfaces of traditional glass containers with a layer of silica to reduce extractables (e.g., Schott Type I Plus®) and glass particles that are produced through delamination. Providing coated articles, however, are cumbersome and expensive and, therefore, not widely accepted in the pharmaceutical packaging market. Thus, there is a need for a cost-effective pharmaceutical packaging glass that exhibits low extractables and leaching with a moderate working point temperature that can be used in pharmaceutical packaging applications.